"Doom is a landmark 1993 first-person shooter video game by id Software. It is widely recognized for having popularized the first person shooter genre, pioneering immersive 3D graphics as well as true third dimension spatiality, networked multiplayer gaming, and support for customized additions and modifications.

The player takes the role of a nameless space marine who has been punitively posted to Mars after assaulting his commanding officer, who ordered his unit to fire upon civilians. The Martian marine base acts as security for the Union Aerospace Corporation (UAC), a multi-planetary conglomerate, which is performing secret experiments with teleportation by creating gateways between the two moons of Mars, Phobos and Deimos. The manual makes it clear that Phobos is considered by space marines to be the dullest assignment imaginable: "with no action for fifty million miles, your day consisted of suckin' dust and watchin' restricted flicks in the rec room." This all changes when the UAC experiments go horribly awry. Computer systems on Phobos malfunction, Deimos disappears entirely, and "something fragging evil" starts pouring out of the gateway, killing or possessing all UAC personnel. Responding to a frantic distress call from the overrun scientists, the Martian marine unit is quickly sent to Phobos to investigate, where the player character is left to guard the hangar with only a pistol while the rest of the group proceeds inside. Over the course of the next few hours, the marine hears assorted garbled radio messages, gunfire, and screams, followed by silence: "Seems your buddies are dead".

The objective of each level is simply to locate the exit room that leads to the next area, marked with an exit sign and/or a special kind of door, while surviving all hazards on the way. Among the obstacles are demonic monsters, pits of toxic or radioactive slime, ceilings that lower and crush the player character, and locked doors for which a keycard, skull-shaped key device, or remote switch must be located. The levels are sometimes labyrinthine and feature plenty of items such as additional ammo, health increases and other "power-ups" along the way, as well as the occasional secret areas which are not immediately obvious as a reward for players who explore more carefully."